Iran's foreign minister accused the United States of involvement in the disappearance of Shahram Amiri, who reportedly worked at a university linked to the elite Revolutionary Guard military corps.
In a sign of the sensitivities surrounding Mr Amiri, Iranian officials have not even publicly identified Mr Amiri as a nuclear scientist, referring to him only as an Iranian citizen.
Mr Amiri's wife has said he was researching medical uses of nuclear technology at a university and was not involved in the broader nuclear programme.
Iran's foreign minister took the unusual step of complaining to the head of the United Nations last week about the disappearance, at the same time raising the case of a former defence minister who vanished in Turkey in 2007, also believed by many to have defected.
Mr Amiri vanished several months before the September revelation of a uranium enrichment facility near the city of Qom, which the United States and its allies accuse Iran of building secretly.
The timing has led experts to question whether Mr Amiri may have given the West information on it or other parts of Iran's nuclear programme.
The discovery of that facility was a coup for Western intelligence.
Iran denied trying to hide the site, insisting it was not yet required to declare it to the UN nuclear watchdog.
Still, it was put on the defensive as it entered landmark nuclear negotiations with the US and other world powers last week, talks that have somewhat eased rising tensions between the two sides.
US officials have said multiple streams of intelligence - particularly spy satellites - were used to reveal the Qom site and its function, but they have not specified whether the sources included Iranians on the ground.
The United States and its allies accuse Iran of secretly seeking to develop nuclear weapons, a claim Iran denies, saying its programme is intended only to produce electricity.
Little is known about Mr Amiri, and his fate remains a mystery after more than four months.
Iran has asked Saudi Arabia for information on his whereabouts but received no reply, Foreign Ministry spokesman Hasan Qashqavi said earlier this week.
Mr Amiri's relatives have demonstrated several times outside the Saudi Embassy in Tehran demanding information.
The Iranians "may be concerned that the Americans were involved in luring him away," said Meir Javedanfar, an Iranian-born analyst based for the Middle East think tank, meepas.
He raised the possibility Mr Amiri was willingly offering information to the West, despite Iranian claims he was arrested in Saudi Arabia.
"There's the possibility he was taken away in a limousine rather than being shoved in the back of a car, meaning that he could have been a walk-in," said Mr Javedanfar, who is based in Israel.
Mr Amiri worked as a researcher at Tehran's Malek Ashtar University, according to Iran's state-run English language channel Press TV.
The university has been cited by the UN in the past as a nuclear research site and is widely thought to be run by the Revolutionary Guard.
One Iranian news website claimed Mr Amiri had worked at the Qom facility and had defected in Saudi Arabia.
Mr Amiri travelled to Saudi Arabia on May 31 for Omra, an Islamic pilgrimage to Mecca, his wife told the unofficial news agency ISNA. The last she heard from him was on June 3, when he called her from the holy city of Medina.
She said he told her that during his arrival in Saudi Arabia, he had been questioned extensively by police at the airport - "more than any other passenger," according to ISNA, which did not give the wife's name.
Foreign Minister Manouchehr Mottaki raised the level of interest, saying that Mr Amiri had been arrested and accused the United States of a role.
"We've obtained documents about US involvement over Shahram Amiri's disappearance," Mr Mottaki said, according to the semiofficial Fars news agency.
"We hold Saudi Arabia responsible for Shahram Amiri's situation and consider the US to be involved in his arrest," Mr Mottaki said, quoted by the official IRNA news agency.
"We regard the Saudi government as responsible for Amiri's condition and according to some documents available for us, we consider that the US is responsible for his detention."
Comments